I don't think it is possible to make the cost lower by technical rules. Manufacturers will always spend as much as they are allowed to even the simplest possible part. Look at S2000 which is in fact very simple formula. All shocks are same without ball bearings, diffs are dumb clutchpacks with none center one, all transmission is highly standardized and limited to just two manufacturers. Cars have steel bodyshells. Carbon is allowed only for covering layer, no titanium allowed etc. There are limited options of homologating new things and even those like ECU software must be homologated. And in the end it's still rather expensive car with differences between works and private one.

It's like in a lumberjack competition. You can buy an axe for 10 Euro but the competition one costs 200 Euro even though it is still an axe.